If you laid San Diego County’s 4,200 square miles end to end, the line would stretch from Honolulu to Chicago. Of the nation’s 3,000 counties, San Diego has the 12th largest farm economy and is the fifth most populous, with its 3.14 million population representing a 10 percent increase over the year 2000.

Its coastline alone stretches 70 miles and takes about 90 minutes to drive.

The last statistic concerns San Diego Coastkeeper the most. A 2011 study by the environmental watchdog said all that size and activity (coupled with the county’s aging drainage infrastructure) has meant increased pollution levels in the county’s 11 watersheds that feed into the Pacific Ocean. But another set of numbers reflects Coastkeeper’s efforts in stemming the flow of the bad stuff — and for one official, the people behind the stats make all the difference in the group’s effectiveness.

One Saturday a month, a core of Coastkeeper volunteers take to the county’s waterways at 40 locations that feed into nine of the 11 area watersheds, loading up on samples for presentation of data to various state and local environmental offices and the Environmental Protection Agency. It’s not as easy as it sounds, because the volunteers do more than gather water — they’re responsible for the actual sample analysis, shoring up state and local governments’ limited collection resources.

Coastkeeper’s water-quality laboratory manager credits the program with making the county’s monitoring effort one of the biggest and best in the state.

“Because our volunteers produce professional-level data,” Travis Pritchard said, “they become a vital part of the Coastkeeper team and of a larger effort by many community, government and corporate stakeholders to understanding San Diego County’s water quality and how to improve it.”

Coastkeeper recently announced its 2013 volunteer monitoring schedule, which begins with training sessions on Jan. 26 and continues March 16, May 18, July 20, Sept. 14 and Nov. 16. The last sample collection of 2012 takes place on Saturday, Dec. 15. Sample collections in 2013 take place beginning Feb. 23 and continue April 20, June 22, Aug, 17, Oct. 19 and Dec. 14.

Founded in 1995, Coastkeeper has been gathering its data since 2000 and has just signed its 700th volunteer. The group’s 2011 watershed report, its first, noted that 85 recruits collected samples reflecting the health of nine watersheds for 2009-10 from the Tijuana River site to just south of Fallbrook. The majority of the watersheds’ health readings fell into the “fair” category.

No county watershed scored in the “marginal” or “excellent” ranges.

While these data may not always augur well, the solutions do — and Pritchard said the volunteers play a vital role to that end for one very important reason.

“Water-quality professionals,” Prit-chard said, “are terrible at getting their data out to the public. I know what you mean about the [colossally thick] reports from places like the [California] Coastal Commission and the EPA. [The volunteers] make the collection process faster from our end and not adding to the backlog. They understand our way of using data to tell a story … We are extremely grateful for them.”

Meanwhile, Pritchard said, he can’t overemphasize the slow but sure impact that development and farming can have on a waterway through the depletion of soils and plants.

“One slab of concrete [or] the loss of crops,” he said, “diverts the natural flow so the waterway will die a death of a thousand cuts.”

But the volunteers put a human face on the sea of numbers that results, quietly assuring that help is on its way.

For a look at Coastkeeper’s watershed report, visit www.sdcoastkeeper.org. For information on how to become a water-quality monitor, email volunteer@sdcoastkeeper.org or call the group’s community engagement coordinator at (619) 758-7743, ext. 131.